Did you validate that the object referenced by
is, indeed, an object of type UILabel? My guess is that it is not and that it is, in fact, an NSCFString type object.
Obviously, if that's the case, you will want to either share more code or do some debugging.
Just out of curiousity, wondering if you're compiling with LLVM and wondering if Xcode, itself, is able to give you any "hints" (read: warnings) about the source of this bug?